1. Field of the Invention
The present invention relates to a multi-layer structure obtained by laminating a layer comprising a conventional polyamide-base resin (e.g., nylon 11, nylon 12) and a layer comprising a specific polyamide resin (nylon 9T) consisting of a terephthalic acid and a nonanediamine. More specifically, the present invention relates to a multi-layer structure excellent in a alcohol gasoline permeation-preventing property, interlayer adhesion, low-temperature impact resistance, heat resistance and chemical resistance.
2. Description of Related Art
In-the field of automobile-related fuel tubes, hose, tanks and the like, formation of lightweight constituent parts of an automobile is proceeding and the main material for these parts is changing from metal to resin in view of rusting due to anti-freezing agent on roads or the recent issue of energy saving. For example, a saturated polyester-base resin, a polyolefin-base resin, a polyamide-base resin and a thermoplastic polyurethane-base resin are used. However, a single layer hose using such a resin is insufficient in the heat resistance, chemical resistance and the like and, therefore, the application thereof is limited.
Furthermore, from the standpoint of preventing environmental pollution, strict regulations regarding exhaust gas have been recently implemented and include preventing volatile fuel hydrocarbons, or the like, from leaking out into air by diffusion through a fuel tube, a hose or a tank. The regulations will become more and more strict in the future and it is required to maximally, prevent the fuel from permeating and diffusion through the fuel tube, hose or tank. Also, from the standpoint of reducing gasoline consumption and attaining higher performance, an oxygen-containing gasoline [hereinafter this may be sometimes simply referred to as “alcohol gasoline”] having blended therein an alcohol having a low boiling point, such as methanol and ethanol, or an ether such as methyl-tert-butyl ether (MTBE), is being used. However, the permeation of this fuel cannot be satisfactorily prevented in shaped articles using a conventional polyamide-base resin alone, particularly nylon 11 or nylon 12 which are excellent in the mechanical strength, toughness, chemical resistance and flexibility. Thus, an improvement is required in the prevention, particularly, of alcohol gasoline permeation.
To more successfully prevent the permeation of alcohol gasoline, the wall thickness of fuel tube, hose or tank must be increased, however, this incurs problems that the fuel pipe system decreases in the flexibility or becomes heavy and furthermore, the material or production cost increases.
In order to solve this problem, a multi-layer structure having disposed therein a resin having good alcohol gasoline permeation-preventing property, such as; ethylene-vinyl alcohol copolymer (EVOH), polymethaxylyleneadipamide (nylon MXD6), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), polyvinylidene fluoride (PVDF), ethylene/tetrafluoroethylene copolymer (ETFE), ethylene/chlorotrifluoroethylene copolymer (ECTFE), tetrafluoroethylene/hexafluoropropylene copolymer (TFE/HFP, FEP) and tetrafluoroethylene/hexafluoropropylene/vinylidene fluoride copolymer (TFE/HFP/VDF, THV), has been proposed (see, for example, International Application Publication No. 93/25835).
The ethylene-vinyl alcohol copolymer (EVOH), polymethaxylyleneadipamide (nylon MXD6) and the like are known to have good adhesive strength to nylon 6, however, the adhesive strength to nylon 11 or nylon 12 which has been conventionally used as a single layer shaped article is insufficient and it is necessary to provide an adhesive layer between layers or apply a specific surface treatment between layers.
Other polyester-base resins and fluororesins are low in the adhesive property to a polyamide resin. Therefore, for example, a technique of using an adhesive resin composition comprising a mixture of a polyester-base resin or fluororesin and a polyamide resin, which are the resins constituting the two layers to be bonded, has been proposed. However, the interlayer adhesion is affected by the morphology of the adhesive resin composition and this gives rise to a problem that the interlayer adhesion is largely dispensed or decreased depending on the production conditions, environmental conditions on use, or the like.
As the adhesive resin, a maleic anhydride-modified polyolefin resin and the like are known. However, these resins are lower in thermal aging resistance than the polyamide resin used and cannot be used in a severe condition. Also, the increase in the number of layers disadvantageously incurs problems in view of cost and process control.
An object of the present invention is to solve these problems and provide a multi-layer structure excellent in the alcohol gasoline permeation-preventing properties and, particularly, hydrocarbon component permeation-preventing properties, and also excellent in the interlayer adhesion, low-temperature impact resistance, heat resistance and chemical resistance.